Adapted description and extended testdata

README.md

@@ -1,21 +1,31 @@
-# Sudoku verifier
+# Validate a Sudoku
 
 ## Definition
-Sudokus are logic number puzzles in which cells in a 9×9 grid must be populated with 
-the digits 1 to 9 in a way that each digit occurrs only once in each unit (that is column, 
-row or block = 3×3 sub grid).
+Sudokus are number-puzzles in which cells in a 9×9 grid must be populated with the numbers `1` to `9`.
+
+The following constraints must apply to the 9×9 grid.
+
+ * Each digit from `1` to `9` only occurs only once 
+    * per row
+    * per column
+    * per block (i.e. 3×3 sub grid)
 
 ![a solved simple sudoku](sudoku.gif)
 
 ## Goal
-Validate if a given solution for a Sudoku is valid, by checking that the digit
-1 to 9 appear only once in column, in each row and in each of the 9 sub grids.
+Validate, if a given Sudoku is a valid solution. 
+
+The Sudoku must comply with the definition above.
 
 ### Input
-a sequence of 81 digits, organized in 9 columns and 9 rows
+A sequence of 81 digits, organized in 9 columns and 9 rows.
+
+The columns of a row are separated by blanks.
+
+Rows are separated by line-breaks.
 
 ### Output
-A boolean value, if the grid is valid.
+A boolean value `true` or `false` defining the correctness of the input.
 
 ### Constraints
 1 <= `digit` <= 9